One of the largest swinging bells in the world, weighing 55 tons (7,850 stone), was unveiled in the Polish city of Krakow on Thursday ahead of being installed at a major pilgrimage site in Brazil.

The "Vox Patris" bell, four metres (13 feet) in height and 4.5 metres in diameter, will eventually be housed in the Basilica of the Eternal Father in the city of Trindade in central Brazil, owner Piotr Olszewski said.

Made from copper and tin, it will be activated by four engines, and once installed will be part of a tower 100 metres high, he added.

"The preparations and tests lasted almost four years," Olszewski told reporters, acknowledging that the first casting at the Metalodlew foundry in Krakow had been a failure.

"The mold did not hold, micro-cracks appeared which caused leaks," he explained.

"It was necessary to start all over again, but the second attempt was successful."

The challenge now is to transport the giant bell to Brazil by boat -- a journey expected to take a year.